In recent years, the installed wind capacity is dramatically increased, thus increasing the need for large-scale permanent magnet electrical rotating machines larger than 1 MW with the aim of increasing the per-machine capacity to achieve greater economy, enhancing the efficiency of generators and reducing size and weight.
For application of a large-scale permanent magnet electrical rotating machine to wind power generation, a long life span of about 20 years is required. Thus, the permanent magnet performance is required to be maintained for about 20 years. For regular permanent magnets, a coating is applied to the surface of the permanent magnet with consideration given to environmental resistance. However, the coating to the magnets of a rotor of the interior permanent magnet structure is disadvantageously damaged when the magnets are inserted. Thus, a member for protecting the coating is required when the magnets are inserted.
Also, in the large scale machines, even if higher efficiency is achieved, the loss results in being high as an absolute value. To avoid this, if it is attempted to obtain a heat density nearly equal to that in small scale machines in order to minimize the loss, an increase in size of the permanent magnet electrical rotating machine is anyhow necessary. The increase in size of the permanent magnet electrical rotating machine results in an increase in weight, leading to an increase of the cost of manufacturing and the cost of building a windmill. As a result, a reduction in size of the permanent magnet electrical rotating machine and an increase in heat density are necessary.
A necessity for realizing an electrical rotating machine with a high heat density is an enhancement of cooling structure. For usual electrical rotating machines without use of permanent magnets, providing a duct is contemplated as a way of solving the problem. However, a large-scale permanent magnet electrical rotating machine provided with a duct has been almost unprecedented, and especially, one with consideration given to the relationship with a magnet protection member has been unprecedented.
Patent Literature 1 discloses the method of obtaining a rotor of an interior permanent magnet motor which prevents damage to a permanent magnet and also has outstanding motor performance.